When SpongeBob shows Mr. Krabs a picture of the Tattletale Strangler, he retreats into his shell in surprise
"Shell of a Man"
Mr. Krabs molts his shell and kicks it in frustration, causing it to fly into SpongeBob, who becomes stuck inside it. SpongeBob later goes to Mr. Krabs' navy reunion with the shell, faking to be Mr. Krabs. At the end of the episode, after Mr. Krabs wins the Trophy of Manly Toughness, he says that his shell will grow back.
Mr. Krabs gives his shell to SpongeBob as a replacement for Gary's shell, costing SpongeBob a year's pay. That night, Mr. Krabs gets cold without his shell and goes to SpongeBob's house to borrow a blanket.